Sattva binds one to happiness, O descendant of Bharata, and rajas binds one to action. But tamas, by veiling knowledge, binds one to negligence.
Explanation
Krishna is explaining how the three qualities of nature (guṇa) each tie the embodied self in a different way. Sattva (clarity, goodness) attaches one to happiness (sukha), rajas (passion, restless energy) to action (karma), and tamas (inertia, darkness) covers over knowledge and leads to negligence or heedlessness (pramāda). The verse sets up the next one, which says that each guna at times overpowers the other two.